1. Introduction: the Scientific Method

The scientific method is typically taught as a step-by-step sequence. Drag the steps below, listed in alphabetical order, into an order that matches steps described in the table.

[qwiz]

[h]Steps of the Scientific Method

[q labels = “top”]

 

Steps of the Scientific Method
_______________________ This is where it begins: Sensing the world, and noticing patterns and relationships
_______________________ This stage involves making an educated guess that includes a prediction,
_______________________ This phase involves a structured form of observation that allows you to examine one thing at a time.
_______________________ This last stage involves answering questions such as 1) Was the hypothesis correct? 2) Are there other lines of evidence that point in the same direction?

 

[l]Drawing conclusions

[fx] No. Please try again.

[f*] Correct!

[l]Formulating hypotheses

[fx] No. Please try again.

[f*] Good!

[l]Making observations

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[l]Performing experiments

[fx] No, that’s not correct. Please try again.

[f*] Great!

[/qwiz]

2. Interactive Reading: A Case Study: The link between cancer and smoking. Initial observations

To learn about the scientific method and experimentation, we’ll look at a very simplified history of the discovery of the link between smoking tobacco and cancer.1

1For a detailed view of this story, follow the links to tobaccocontrol.bmj.com at the end of this tutorial. Much of the information below comes from that site.

[qwiz qrecord_id=”sciencemusicvideosMeister1961-Controlled Experiments 1: Cancer and Smoking 1″]

[h]Interactive Reading: The Link between Cancer and Smoking

[i]Carefully read what follows, dragging in the words on top to the right place.

[q labels = “top”]

05_tobacco_large_EU_lung_02_en_medium
Healthy lungs (left). Lungs impacted by smoking (right). (Courtesy of World Health Organization, permission pending)

It hasn’t always been known that smoking tobacco caused lung-cancer. In the 1500s, tobacco was praised for its supposed health benefits. Lung cancer itself was once extremely _______. But mechanical production of cigarettes, free distribution of cigarettes to soldiers, and mass marketing caused a global lung cancer ____________ that began in the 1900s and continues today.

The first observations of the cancer/smoking connection started around 1900. The key observation was the rise in _______ cancer rates. Among the first to notice this connection was a German medical student, Hermann Rottman, who noticed higher rates of lung cancer among German __________ workers. Rottman suspected that exposure to tobacco dust was causing cancer.

 

[l]epidemic

[fx] No. Please try again.

[f*] Excellent!

[l]lung

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]rare

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]tobacco

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[q labels = “top”]

By the 1920s, the increasing rate of lung cancer began to be linked with _________, but other possible causes for increased lung cancer rates were also considered. These included exposure to poison gas suffered by soldiers during World War One, and exposure to the tar that was increasingly used on roads as driving became more common.

In the 1930s, population studies in German hospitals led to the discovery that lung cancer patients were far ___________ to have smoked than patients who didn’t have cancer. By the 1950s, American doctors were able to calculate that “smokers of 35 cigarettes per day increased their odds of ________ from lung cancer by a factor of 40.” (tobaccocontrol.bmj.com).

So, by that point there was a clear __________: if someone smokes, then they have a higher chance of developing lung cancer. Now let’s look how experiments could be designed to confirm that hypothesis.

[l]dying

[fx] No. Please try again.

[f*] Great!

[l]hypothesis

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]more likely

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]smoking

[fx] No, that’s not correct. Please try again.

[f*] Good!

[/qwiz]

3. Controlled Experiments: General Features

For the sake of simplicity (and learning), the experiment described below is somewhat different from the actual animal experiments that were performed to help establish the link between tobacco smoke and cancer.

Let’s start by reviewing what an experiment is: it’s a controlled form of observation that lets you observe one thing at a time. As you read what follows, refer to the diagram below.

experiment design
Structure of a controlled experiment

[qwiz style = “width: 528px; min-height:0px; border: 3px solid black; ” qrecord_id=”sciencemusicvideosMeister1961-Controlled Experiments: General Features”]

[h]Quiz: Controlled Experiments, General Features

[q] Experiments try to test the effect of ONE thing at a time. The thing that you test is called the independent variable. 

In relationship to our hypothesis (if someone smokes, they have a higher chance of developing lung cancer), what’s the independent variable?

[c] lung cancer

[c*] tobacco smoke

[f]No. Lung cancer is what happens in response

[f]Yes. In relationship to our hypothesis, the independent variable is tobacco smoke. It’s the thing that we’re going to test.

[q]Because we’re testing a harmful substance, we’re not going to test humans, but animals related to humans (like mice or rats). Keep that in mind when we talk about “groups” and “individuals” below.

  1. One group is the control group. The control group is
    1. the standard for comparison.
    2. not exposed to the independent variable.
  2. The second group is the experimental group. This group gets exposed to the independent variable.

In relationship to our hypothesis about smoking and cancer, what will be our control group?

[c]The rats that are exposed to tobacco smoke.

[c*]The rats that are not exposed to tobacco smoke

[c]Any rats that develop cancer will make up the control group.

[f]No. If our independent variable is tobacco smoke, then the rats exposed to tobacco smoke are the experimental group.

[f]Excellent. If our independent variable is tobacco smoke, then the rats that are NOT exposed to tobacco smoke are the control group (they’re not exposed to the independent variable)

[f]No. This question is about the groups you set up to test the independent variable. Development of cancer is a possible effect of the independent variable, but it’s not connected with the design of your experiment.

[q] What’s the experimental group?

[c*]The rats that are exposed to tobacco smoke.

[c]The rats that are not exposed to tobacco smoke

[f]Correct. That rats that are exposed to tobacco smoke will make up the experimental group.

[f]No. The rats that are not exposed to tobacco smoke make up the control group.

[q]An experiment is going to have some observable outcome. That outcome is called the dependent variable. In relationship to our hypothesis (if someone smokes, they have a higher chance of developing lung cancer), what’s the dependent variable?

[c]tobacco smoke

[c*]the rate of lung cancer

[f]No. Tobacco smoke is the independent variable (the thing that we’re testing).

[f]Yes. The rate of lung cancer is the dependent variable (it’s what’s caused by the independent variable, which is tobacco smoke.

[x]

[/qwiz]

4. Scientific Method and Experimental Design Flashcards

To make sure you understand the key terms we’ve used in this lesson, work through these flashcards. Flashcards can feel very difficult, but they’re incredibly effective in helping you to remember what you’ve learned. Be very honest with yourself as you use these cards. It’s much better to study a card twice than to rush through without learning the material.


[qdeck style=”width: 528px; border: 2px solid black; ” qrecord_id=”sciencemusicvideosMeister1961-Controlled Experiments Flashcards”]

[h] Flashcards: The Scientific Method and Controlled Experiments

[i] Instructions.

  • Click ‘Flip’ to see the answer to each card.
  • If you know it, click ‘Got it.”
  • If you don’t know it as well as you’d like, click ‘Need more practice,’ and that card will go to the bottom of the deck so you can practice it again.
  • ‘Shuffle’ lets you shuffle the deck.

[!]Card 1++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++[/!]

[q] The step in the scientific method that involves sensing the world, and noticing patterns and relationships is  [textentry]

[a]The step in the scientific method that involves sensing the world, and noticing patterns and relationships is observation.

[!] CARD 2++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++[/!]

[q]An educated guess that includes a prediction is a _______________

[textentry]
[a]An educated guess that includes a prediction is a hypothesis.

[!] CARD 3++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++[/!]

[q]A structured form of observation that allows you to examine one thing at a time is a(n) _______________

[textentry]
[a]A structured form of observation that allows you to examine one thing at a time is a(n) experiment

[!] CARD 5++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++[/!]

[q]An experiment tests the validity (or correctness) of a(n) _______________

[textentry]
[a]An experiment tests the validity of a hypothesis.

[!] CARD 6++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++[/!]

[q]A well-formulated hypothesis includes a __________

[textentry]
[a]A well-formulated hypothesis includes a prediction

[!] CARD 7++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++[/!]

[q]The thing you test in an experiment is the _________

[textentry]
[a]The thing you test in an experiment is the independent variable

[!] CARD 8++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++[/!]

[q]The measured or observed result of the independent variable is the ___________

[textentry]
[a]The measured or observed result of the independent variable is the dependent variable.

[!] CARD 9++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++[/!]

[q]A student performs an experiment to test the effect of red light on plant growth. The independent variable is ________

[textentry]

[a]A student performs an experiment to test the effect of red light on plant growth. The independent variable is red light

[!] CARD 10++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++[/!]

[q]A student performs an experiment to test the effect of red light on plant growth. The student’s hypothesis is that red light will produce more growth than normal light. What would be a logical control group?

[textentry]

[a]A student performs an experiment to test the effect of red light on plant growth. The student’s hypothesis is that red light will produce more growth than normal light. A logical control group would be plants exposed to normal light.

[!] CARD 11++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++[/!]

[q]A student performs an experiment to test the effect of red light on plant growth. The student’s hypothesis is that red light will produce more growth than normal light. What would be a logical experimental group?

[textentry]

[a]A student performs an experiment to test the effect of red light on plant growth. The student’s hypothesis is that red light will produce more growth than normal light. A logical experimental group would be plants exposed to red light.

[x]

If you want more practice, please press the restart button below. Otherwise, follow the links below.
[restart]
[/qdeck]

5. A controlled experiment to test the smoking/cancer connection

So, how would this work in the case of an animal experiment to test the hypothesis that tobacco smoke causes cancer?

Well, if it’s an animal experiment, we need an animal.

02_rat
Rat

Like humans, rats are mammals. Their internal organs, including their lungs, look very much like miniature versions of those in humans. In terms of body chemistry, they’re also very much like us: many of the chemical reactions occurring in our cells are identical. So the reasoning (which is widely accepted in biology) is that if something causes cancer in a rat, it is likely to cause cancer in a human being.

[qwiz style = “width: 528px; min-height:0px; border: 3px solid black; ” qrecord_id=”sciencemusicvideosMeister1961-Controlled Experiments: Quiz 2″]

[h]Using the Scientific method

[q]So here’s our experiment. We’re going to have two rats. In one group, we’ll have a rat that smokes. In the second group, we’ll have a rat that’s exposed to exactly the same conditions (the same food, temperature, etc.). The only difference is that the second rat won’t smoke.

a non-smoking rat  a smoking rat

What’s the problem with this experiment?

[c] There’s no control group

[c] There’s no experimental group

[c] There’s no independent variable

[c*]The groups are too small.

[f] Nope: The control group is the non-smoking rat. As with all control groups, it’s not exposed to the independent variable (tobacco smoke). But there’s still a big problem with this design. What if the rat in the control group was an unlucky rat that developed cancer without smoking (as sometimes happens)? What if the rat in the experimental rats was one of those lucky individuals who can be exposed to tobacco smoke and never develop cancer? What can you do to improve the design?

[f] That’s not right. The experimental group is the smoking rat. As with all experimental groups, it’s being exposed to the independent variable, tobacco smoke.But there’s still a big problem with this design.What if the rat in the control group was an unlucky rat that developed cancer without smoking (as sometimes happens)? What if the rat in the experimental rats was one of those lucky individuals who can be exposed to tobacco smoke and never develop cancer? What can you do to improve the design?

[f] Incorrect. The independent variable is tobacco smoke. But there’s still a big problem with this design.

[f] Correct! In a well-designed experiment, you have to overcome the problem of random differences in your subjects (the rats, in this case). Having only one rat in each group could result in a situation where the control rat happens to be a rat that randomly develops cancer, and the experimental rat happens to be one that’s resistant to cancer (despite the fact that it’s exposed to tobacco smoke). You need to have large groups.

[q]So, here’s what we’re going to do: We’re going to use two groups of rats, each with enough individuals to show the effect of the independent variable. One group will be exposed to tobacco smoke. A second group will be kept under identical conditions, except for the fact that it won’t be exposed to tobacco smoke. We’re going to measure the rate of cancer in each group, and see if there’s a difference.

If there is a difference, we can be pretty sure that it’s a result of the presence of the independent variable (tobacco smoke). This difference, because it depends on the effect of the independent variable, is called the dependent variable.

What’s the control group in this experiment?

[c]The rats exposed to tobacco smoke.

[c*]The rats not exposed to tobacco smoke, but otherwise kept in the same conditions.

[c]Tobacco smoke.

[c]The rate of lung cancer in the control and experimental group.

[f]No. The rats exposed to tobacco smoke make up the experimental group.

[f]Yes. The rats that are not exposed to tobacco smoke (the independent variable) make up the control group.

[f]No. Tobacco smoke is the independent variable.

[f]No. The rate of lung cancer is the dependent variable.

[q]

What’s the experimental group in this experiment?

[c*]The rats exposed to tobacco smoke.

[c]The rats not exposed to tobacco smoke, but otherwise kept in the same condition.

[c]Tobacco smoke.

[c]The rate of lung cancer in the control and experimental group.

[f]Yes. The rats exposed to tobacco smoke make up the experimental group.

[f]No. The rats that are not exposed to tobacco smoke (the independent variable) make up the control group.

[f]No. Tobacco smoke is the independent variable.

[f]No. The rate of lung cancer is the dependent variable.

[q]

What’s the dependent variable in this experiment?

[c]The rats exposed to tobacco smoke.

[c]The rats not exposed to tobacco smoke, but otherwise kept in the same condition.

[c]Tobacco smoke.

[c*]The rate of lung cancer in the control and experimental group.

[f]No. The rats exposed to tobacco smoke make up the experimental group. The dependent variable is what’s caused by the independent variable (tobacco smoke). Tobacco smoke will be associated with ….

[f]No. The rats that are not exposed to tobacco smoke (the independent variable) make up the control group. The dependent variable is what’s caused by the independent variable (tobacco smoke). Tobacco smoke will be associated with ….

[f]No. Tobacco smoke is the independent variable. The dependent variable is what’s caused by the independent variable (tobacco smoke). Tobacco smoke will be associated with ….

[f]Yes. The rate of lung cancer is the dependent variable.

[q]What’s the independent variable in this experiment?

[c]The rats exposed to tobacco smoke.

[c]The rats not exposed to tobacco smoke, but otherwise kept in the same condition.

[c*]Tobacco smoke.

[c]The rate of lung cancer in the control and experimental group.

[f]No. The rats exposed to tobacco smoke make up the experimental group. The independent variable is the thing that we’re testing. What are we testing in this experiment?

[f]No. The rats that are not exposed to tobacco smoke (the independent variable) make up the control group.The independent variable is the thing that we’re testing. What are we testing in this experiment?

[f]Yes. Tobacco smoke is the independent variable.

[f]No. The rate of lung cancer is the dependent variable. The independent variable is the thing that we’re testing. What are we testing in this experiment?

[x]

[/qwiz]

6. What Happened Next

Animal studies like the one described above confirmed the hypothesis that rats exposed to tobacco smoke will have higher rates of cancer. In fact, this had been known since the 1930s, when controlled experiments showed that elements of tobacco smoke, when put into liquid form, could cause tumors to form on the skin of rabbits.

Throughout the 1900s, several lines of evidence confirmed the tobacco/cancer link. These lines of evidence included

  • Chemical analysis of tobacco to identify cancer causing agents,
  • Studies of how cells in lung tissue were affected by smoking, and
  • Public health studies showing that people who smoked were more likely to develop lung cancer.

However, through much of the 1900s, smoking continued to increase among many populations around the world. This was largely caused by tobacco companies, which continued to market cigarettes, and which devoted significant amounts of resources to denying the scientific evidence about the danger of smoking. You can read the entire story by following the links at the bottom of this tutorial.

7. Checking Understanding Quiz

In this tutorial, we’ve learned about

  1. The steps of the scientific method
    1. Observe
    2. Hypothesize
    3. Experiment
    4. Draw conclusions
  2. The design of a controlled experiment
    1. independent variable
    2. dependent variable
    3. control group
    4. experimental group
  3. Some additional features of a well-designed experiment
    1. It tests only one thing (the independent variable)
    2. It uses large enough groups to avoid random results based on individual differences.

To make sure you’ve mastered this material, take the quiz below.

[qwiz style = “border: 3px solid black; ” qrecord_id=”sciencemusicvideosMeister1961-Controlled Experiments: Checking Understanding”]

[h]Quiz: The Scientific Method and Designing Experiments
[i] Here’s how the quiz works:

  • Each question is multiple choice, but the entire quiz is like a series of flashcards.
  • If you get the question right, it comes off the deck.
  • If you get the question wrong, it goes to the bottom of the deck, so you can try it again.

[!] Question 1++++++++++++++[/!]

[q] Noticing patterns in the world around you is best classified as

[c*]making an observation

[c]asking a question

[c]formulating a hypothesis

[c]performing an experiment

[f] Yes. Noticing patterns in the world around you is best classified as making an observation.
[f] No. Noticing patterns is the first step in the scientific method, even before asking questions.
[f] No. Noticing patterns is the first step in the scientific method. What is that first step?
[f] No. Noticing patterns is the first step in the scientific method. What is that first step?

[!] Question 2++++++++++++++[/!]

[q] An educated guess that includes a prediction is a(n)

[c] observation

[c*] hypothesis

[c] experiment

[f] No. Observations lead to questions. After questions, we formulate educated guesses. What are these called?
[f] Excellent! An educated guess that includes a prediction is a hypothesis.
[f] No. Experiments are performed in order to prove a ______________.

[!] Question 3++++++++++++++[/!]

[q] A structured form of observation that allows you to observe one thing at a time is a(n)

[c] observation

[c] hypothesis

[c*] experiment

[f] No. An observation is simply sensing the world. The special kind of observation described above would follow formulation of a hypothesis. What follows a hypothesis?
[f] No. A hypothesis is an educated guess that includes a prediction. You’re looking for the activity the is used to confirm a hypothesis.
[f] Nice. A structured form of observation that allows you to observe one thing at a time is an experiment.

[!] Question 4++++++++++++++[/!]

[q] This includes a prediction, and is best put in an “if…then…” format

[c] observation

[c*] hypothesis

[c] experiment

[f] No. An observation is simply sensing the world, and noting what you sense. In the case of cancer and smoking, the observation was something like “we’re noticing that there are many more cases of lung cancer than we’re used to seeing.”
[f] Yes. A hypothesis is an educated guess that includes a prediction, often phrased in “if…then…” format.
[f] No. An experiment is designed to confirm a prediction. The “if…then…” prediction is part of an earlier stage of the scientific method.

[!] Question 5++++++++++++++[/!]

[q] This part of the scientific method involves testing the whether a hypothesis is correct.

[c]observation

[c]drawing a conclusion

[c*]experiment

[f]No. An observation comes before formulating a hypothesis (much less testing it).
[f]No. You can’t draw a conclusion until you’ve confirmed a hypothesis. How do you confirm a hypothesis?
[f]Yes. An experiment is designed to confirm whether a hypothesis is correct or not

[!] Question 6++++++++++++++[/!]

[q]In an experiment, the thing you’re testing is the

[c*]independent variable

[c]dependent variable

[c]control group

[c]experimental group

[f]Yes. In an experiment, the thing you’re testing is the independent variable.
[f]No. The dependent variable is the result you get. It depends on the thing you’re testing, which is called the…
[f]No. The control group is the group that is NOT exposed to the independent variable. It’s the standard for comparison. And if you look closely, you’ll see that I just gave away the answer to this question.

[f]No. The experimental group is the group that is exposed to the independent variable. And if you look closely, you’ll see that I just gave away the answer to this question.

[!] Question 7++++++++++++++[/!]

[q]In an experiment, the measured result is the

[c]independent variable

[c*]dependent variable

[c]control group

[c]experimental group

[f]No. In an experiment, the independent variable is the thing you’re testing.
[f]Yes. The dependent variable is the result you get.
[f]No. The control group is the group that is NOT exposed to the independent variable. This question is asking you about results.

[f]No. The experimental group is the group that is exposed to the independent variable. This question is asking you about results.

[!] Question 8++++++++++++++[/!]

[q]The part of the experiment that serves as a standard for comparison, and which shows you what the result would be without the independent variable, is the

[c]hypothesis

[c]dependent variable

[c*]control group

[c]experimental group

[f]No. The hypothesis is the educated guess/prediction that your experiment is trying to prove (or disprove)
[f]No. The dependent variable is the result you get.
[f]Yes. The control group is the standard for comparison. It shows you what the result would be without the independent variable.

[f]No. The experimental group is the group that is exposed to the independent variable. What’s the group that doesn’t get exposed to the independent variable?

[!] Question 9++++++++++++++[/!]

[q]Two students have designed an experiment to test the effect of loud bass notes on reproduction rates in guppies (a small aquarium fish). They divide the guppies into two groups of 15, each group in its own 20 gallon aquarium tank. One tank is exposed to the loud bass notes, and one is not.

In this experiment, which of the following is the independent variable?

[c]the guppies exposed to the low bass notes.

[c]the guppies NOT exposed to the low bass notes.

[c*]the low bass notes.

[c]the rate of reproduction

[f]No. The independent variable is the thing you’re testing. What’s being tested?
[f]No. The independent variable is the thing you’re testing. What’s being tested?
[f]Yes.The independent variable is the thing you’re testing. What’s being tested here is the low-frequency sound.

[f]No.The independent variable is the thing you’re testing. What’s being tested?

[!] Question 10++++++++++++++[/!]

[q]Two students have designed an experiment to test the effect of low bass notes on reproduction rates in guppies (a small aquarium fish). They divide the guppies into two groups of 15, each group in its own 20 gallon aquarium tank. One tank is exposed to the low bass notes, and one is not.

In this experiment, which of the following is the dependent variable?

[c]the guppies exposed to the low bass notes

[c]the guppies NOT exposed to the low bass notes

[c]the low bass notes

[c*]the rate of reproduction

[f]No. The dependent variable is the result you get. These experimenters want to see if low bass notes affect something. What is that something?
[f]No. The dependent variable is the result you get. These experimenters want to see if low bass notes affect something. What is that something?
[f]No. The dependent variable is the result you get. These experimenters want to see if low base notes affect something. What is that something?

[f]Yes. The dependent variable is the result you get. These experimenters want to see if low bass notes affect reproduction rates. Therefore reproduction rates are the independent variable.

[!] Question 11++++++++++++++[/!]

[q]Two students have designed an experiment to test the effect of low bass notes on reproduction rates in guppies (a small aquarium fish). They divide the guppies into two groups of 15, each group in its own 20 gallon aquarium tank. One tank is exposed to the low bass notes, and one is not.

In this experiment, which of the following is the control group?

[c]the guppies exposed to the low bass notes

[c*]the guppies NOT exposed to the low bass notes

[c]the low bass notes

[c]the rate of reproduction

[f]No. The control group is the group that is not exposed to the independent variable. Just figure out what the independent variable is (it’s what you’re testing), and you’ll have your answer.
[f]Nice. The control group is the group that is not exposed to the independent variable. In this experiment, it’s the group not exposed to low bass notes
[f]No. The control group is the group that is not exposed to the independent variable. Just figure out what the independent variable is (it’s what you’re testing), and you’ll have your answer.

[f]No. The control group is the group that is not exposed to the independent variable. Just figure out what the independent variable is (it’s what you’re testing), and you’ll have your answer.

[!] Question 12++++++++++++++[/!]

[q]Two students have designed an experiment to test the effect of low bass notes on reproduction rates in guppies (a small aquarium fish). They divide the guppies into two groups of 15, each group in its own 20 gallon aquarium tank. One tank is exposed to the low bass notes, and one is not.

In this experiment, which of the following is the experimental group?

[c*]the guppies exposed to the low bass notes

[c]the guppies NOT exposed to the low bass notes

[c]the low bass notes

[c]the rate of reproduction

[f]Yes. The experimental group is the group that is exposed to the independent variable. In this experiment, the independent variable is the low bass notes, and the guppies exposed to this sound make up the experimental group.
[f]No. The experimental group is the group that is exposed to the independent variable.Just figure out what the independent variable is (it’s what you’re testing), and you’ll have your answer. 
[f]No. The experimental group is the group that is exposed to the independent variable.Just figure out what the independent variable is (it’s what you’re testing), and you’ll have your answer.

[f]No. The experimental group is the group that is exposed to the independent variable.Just figure out what the independent variable is (it’s what you’re testing), and you’ll have your answer.

[!] Question 13++++++++++++++[/!]

[q]Bob wants to test whether lemon juice can keep dandelion weeds from growing in his garden.He creates several solutions of lemon juice. He then takes dandelion seeds and sprouts them on paper towels. Each day, he sprays the same amount of each solution on the seeds. The data are shown above.

Solution Number of Seeds Percentage of seedlings that sprout
10% lemon juice 15 42%
30% lemon juice 15 44%
50% lemon juice 15 41%

Based on the data, what’s the problem with the design of Bob’s experiment

[c]He had no dependent variable

[c]He has more than one independent variable

[c*]He had no control group

[c]the sample size is too small

[f]No. The dependent variable is the outcome, and Bob’s experiment has a clear outcome (the percentage of seeds sprouting)
[f]No. He’s testing various concentrations of the same thing, which is a fine procedure.
[f]Yes. There’s no control group. Without a control group, it’s impossible to know whether having about 40% of seedlings sprouting is a result of the lemon juice, or whether that’s normal for dandelion seeds.

[f]No (but that’s a smart response). It takes a lot of statistical knowledge to determine the right sample size. 15 might be okay. But, there’s a much bigger problem with this experiment.

[!] Question 14++++++++++++++[/!]

[q]Clara is testing whether iron pills will help skinny dogs gain weight. For her experiment, she takes three dogs, a poodle, a boxer, and a collie. She adds iron to their food for two weeks, and then records their weight. Here are her results

Dog Breed Number of 5 gram iron pills Weight gain (kilograms)
Poodle 1 4
Boxer 3 2
Collie 5 6

Based on the data, what’s the problem with the design of her experiment

[c]She had no dependent variable

[c*]She has more than one independent variable

[c]She has a clear bias toward Collies.

[f]No. The dependent variable is the outcome, and Clara’s experiment has a clear outcome (weight gain). Think about how many things she’s testing.
[f]Yes. She’s using dogs of different breed, and giving them different number of pills, which means that she’s testing at least two things.
[f]No. There’s no evidence for claiming that she’s biased. But think about how many things she’s testing…

[x]

If you want to take this quiz again, click the button below

[restart]


[/qwiz]


If you need more practice, please scroll up to the top and work through this tutorial again. Otherwise, follow the links below:

8. The Scientific Method Song: Interactive Lyrics

This is an interative reading of the lyrics to the Scientific Method Song. If you’re completing this tutorial on your own, and you want to watch the video, then click here (the link will open in a new tab). But if you’re in class, please check with your teacher first!

[qwiz qrecord_id=”sciencemusicvideosMeister1961-Controlled Experiments: Scientific Method Song, Interactive Lyrics”]

[h]Interactive Lyrics, Scientific Method Song

[i]

[q labels=”top”]

Science always begins with a ___________
Inspired by an ___________,
Next step, as you might surmise,
Is to take your question and hypothesize,

 

A _____________should include a prediction,
An educated guess in a form of “if … then”
Like if science rapping is a memory aid
Then better retention will be displayed.

 

Now hypothesis set, you’re ready for next step
Performance of an experiment,
The independent variable’s what you __________
_____________variable’s the result you get

 

[l]dependent

[fx] No. Please try again.

[f*] Great!

[l]hypothesis

[fx] No. Please try again.

[f*] Correct!

[l]observation

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]question

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]test

[fx] No. Please try again.

[f*] Great!

 

 

[q labels=”top”]
CHORUS:
If you want to do science
Use the scientific method
_________,
____________,

Then __________
If you want to do science,
You better do it right!

 

[l]experiment

[fx] No. Please try again.

[f*] Good!

[l]hypothesize

[fx] No. Please try again.

[f*] Good!

[l]observe  

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[q labels=”top”]

Now science well-done’s about taking __________

Because clear results, that’s your ultimate goal.

To see if what you’re testing is the _______ of an effect,

Your design has to be perfect.

 

Use two groups: __________and experimental:
Experimental gets your independent variable
Control group’s the same except for one move:
The independent ____________gets ______________.


Like to prove tobacco smoke is a cause of cancer,

A good experiment will bring you the answer,
Take two groups of guinea pigs or rats to test
And make the groups ______, that’s statistically best

 

[l]control

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]large

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]removed

[fx] No. Please try again.

[f*] Correct!

[l]variable

[fx] No. Please try again.

[f*] Excellent!

[l]cause

 

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[q labels=”top”]

You gotta make ’em big, cause there’s always random stuff,
So a small group of ____________is never enough!
You can get cancer even though you’ve never smoked
But a single __________, well that’s just an anecdote.


So set up two cages exactly the same,

Controlling variables is the name of the game,
Experimental group to smoke gets exposed,
Cause that’s the _______________variable you proposed.

 

[l]case

[fx] No. Please try again.

[f*] Great!

[l]independent

[fx] No. Please try again.

[f*] Good!

[l]subjects

[fx] No. Please try again.

[f*] Great!

 

[q]BRIDGE:
But I’m not saying science is always the way to get to the _______
It won’t tell you whom to ______ or what path to pursue
But amidst all this superstition and deceit
It gives you a path to consult
To cut through all the lies and confusion,
And help you to come to your own __________

[l]conclusion

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]love

[fx] No. Please try again.

[f*] Great!

[l]result

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[q labels=”top”]

Your control group is smoke-free cause that’s how you’ll tell
‘Bout the effect of your independent variable
After enough time you’ll __________your subjects
To see if between them’s a cancer rate _____________,

 
Cause cancer rate’s your ___________ variable,
It’s what’s caused by the ___________ variable,
Which is this case was smoke from tobacco leaves,
Which you forced the experimental group to breathe

[l]dependent

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]difference

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]examine

[fx] No. Please try again.

[f*] Excellent!

[l]independent

 

[fx] No. Please try again.

[f*] Excellent!

[q labels=”top”]

 

And sure it was second-hand smoke that you tested,
So maybe your results will be ____________.
This happens to scientists all of the time,
Whenever there’s a __________in their design.

 

Last step: try to publish in a scientific ________________,
As you try to win science fame eternal.
It’s a never-ending process, and it’s awfully demanding.
But that’s how we build scientific ___________________

[l]contested

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]flaw

[fx] No. Please try again.

[f*] Good!

[l]journal

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]understanding

[fx] No. Please try again.

[f*] Correct!

[/qwiz]

9. Next steps (reading about “The Shameful Past…”)